A term used in sociolinguistics and stylistics to refer to any system of linguistic expression whose use is governed by situational variables. In some cases, the situational distinctiveness of the language may be easily stated, as in many regional and occupational varieties; in other cases, as in studies of social class, the varieties are more difficult to define, involving the intersection of several variables. [Crystal 1997: 408]

ancestorVariety is the predicate expressing the basic diachronic relationship between a language variety that existed some time in the past and a variety existing at a later time such that the former has evolved into the latter through regular language change.

geneticallyRelated is the basic kinship relation between languages varieties. If two language varieties are genetically related, then this implies that both varieties are derived from a common proto-language.

mutuallyIntelligible is the binary, symmetric relation holding between two language varieties such that speakers of the first variety can communicate with members of the second with relative ease, and vice versa.

parentVariety is the relation of direct genetic relatedness, where there are no intermediate ancestors between the ancestor and descendant. For example, Old English is the parent variety of Middle English.